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Winemakers across the North Coast are reporting a relatively normal grape-growing season so far as the crop moves into the crucial stage from flowering to fruit set.

Growers and vintners said the 2016 crop appears larger than last year’s low yield of 402,489 tons in Sonoma, Napa, Mendocino and Lake counties, which was down 24 percent from the 2014 harvest.

Last year, cooler weather in April and May prolonged flowering that led to fruit set, when small flowers on the vines are fertilized and transformed into tiny grapes. The result was a poor fruit set that led to shatter, where fruit clusters do not develop fully, or an uneven ripening of grapes — called “hens and chicks” in the terminology of growers.

“Everything is kind of normal,” said Duff Bevill, owner of Bevill Vineyard Management in Healdsburg, which farms 1,000 acres throughout Sonoma County. “So far, so good.”

Adam Lee, winemaker at Siduri Wines in Santa Rosa, said he thinks the pinot noir crop is about average, while zinfandel and syrah are a little bit below normal.

“It is better than last year. It’s not a giant crop by any means,” Lee said.

This year’s crop has benefited from adequate winter rains, no frost this spring and mostly temperate weather during bloom, said Garrett Buckland, a partner at Premiere Viticultural Services in Napa. He added that fruit set should be completed in Napa County within a week.

“For most varieties, the fruit set looks very good,” Buckland said. “In some cases, the cluster number is lower.”

Still, vintners are looking to get any edge on improving yield. Buckland noted that some growers resort to strategically timing the spread of fertilizer, while others pinch vine tips to energize the vines.

“There are a lot of little tricks and other things we can do to increase our odds,” he said. “In the end, Mother Nature bats last.”

Over at Kunde Family Winery in Kenwood, vintners are attempting a relatively new procedure in which a tractor drives through vines with a heat blower that shoots out a quick blast of heat — up to 350-degree air — to hasten the flowering process.

So far, the test project seems to be working. Winemaker Zach Long noted that a merlot block treated with the heat has reached about 90 percent of fruit set, while a similar untreated block is at 60 percent. The winery also is treating two blocks of chardonnay that have mostly reached fruit set. Overall, the winery uses about 2,000 tons of grapes in its wines annually.

“It’s already had a huge difference,” Long said. He noted that problem fruit set is his second biggest worry as a winemaker, right after frost.

The company that performs the service, Agrothermal Systems of Walnut Creek, contends a trial conducted in 2013 in Oregon, Washington and New Zealand showed the treatment increased the number of berries set per bunch by an average of 24 percent compared to those that were untreated.

Pilot tests also have shown that heat-treated grapes result in wine with better color and tannin structure, said Tim Matson, director of operations for Agrothermal Systems.

“We’re giving it a thermal shock instantaneously. Nothing in nature does that,” Matson said.

Last week, when the chardonnay went into bloom at Kunde, there were a few overcast days along with a high threat of mildew, Matson said. He said the extra heat sped up the process.

“Once it gets pollinated, then we bring it to a temperature that we’re not getting (in nature) to set the fruit,” he said.

Even with the good prognosis so far, vintners cautioned that conditions can turn quickly with the weather as the growing season heads into summer. The next step is veraison, the French term that describes the visual onset of ripening.

“Mother nature will always win,” said Long.

You can reach Staff Writer Bill Swindell at 521-5223 or bill.swindell@pressdemocrat.com. On Twitter @BillSwindell.